Dense Wavelength-Division Multiplexing (DWDM) Network and Method

ABSTRACT

A dense wavelength-division multiplexing (DWDM) optical network comprises an optical bus, which includes an optical source configured to generate a plurality of unmodulated optical signals each having a different wavelength; an optical multiplexer configured to multiplex the unmodulated optical signals to produce a combined, unmodulated optical signal, and to transmit the combined, unmodulated optical signal through an optical fiber; a plurality of nodes connected in sequence to the output of the optical multiplexer. The plurality of nodes are connected by the optical fiber. A DWDM optical network and a method of operation of the DWDM optical network are also disclosed therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional Application No. 62/343,678, filed on May 31, 2016 and entitled “Ring Network with Centralized Dense Wavelength-Division Multiplexing (DWDM) Laser Source” which is hereby incorporated by reference herein as if reproduced in its entirety.

BACKGROUND

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. Intuitively, a wavelength can be thought of as a particular “color”. Many colors can be passed down a single fiber and then separated out at the receiving end back into its constituent colors. Each of those colors can in turn be converted back into an electronic signal. This technique enables bidirectional communications over one strand of fiber, as well as a multiplication of capacity.

Dense wavelength division multiplexing (DWDM) refers originally to optical signals multiplexed within the 1550 nm band so as to leverage the capabilities and cost of erbium doped fiber amplifiers (EDFAs). EDFAs may amplify any optical signal in their operating range.

Conventional dense wavelength-division multiplexing (DWDM) optical systems include stacks of optical line-cards and an optical multiplexer (MUX)-card. Those cards may be fitted on a board used at each end of a DWDM link known as ‘transponders’, which each transponder converts a signal from normal ‘gray’ optics into the specific color for a given channel. Routers or switches are normally connected to the transponders. The optical line-cards transmit high-speed modulated DWDM optical signals. The optical MUX card multiplexes all DWDM wavelengths transmitted from the optical line-cards into an optical fiber for transportation over an optical link or an optical network.

SUMMARY

An example embodiment includes an optical bus for a dense wavelength-division multiplexing (DWDM) network, the optical bus comprising: an optical source configured to generate a plurality of unmodulated optical signals each having a different wavelength; an optical multiplexer configured to multiplex the unmodulated optical signals to produce a combined, unmodulated optical signal, and to transmit the combined, unmodulated optical signal through an optical fiber; and a plurality of nodes connected in sequence to the output of the optical multiplexer.

Optionally, in any of the preceding embodiments, the optical bus wherein each of the plurality of the nodes is not equipped with an optical source.

Optionally, in any of the preceding embodiments, the optical bus wherein each of the plurality of the nodes is equipped with a plurality of optical receivers each configured to detect a respective wavelength of an optical signal.

Another embodiment includes a dense wavelength-division multiplexing (DWDM) optical network comprising: at least two counter-propagating DWDM buses, each of which comprising: a laser bank configured to generate a plurality of unmodulated optical signals each having a different wavelength channel; an optical multiplexer configured to multiplex the unmodulated optical signals to produce a combined, unmodulated optical signal, and to transmit the combined, unmodulated optical signal through an optical fiber for transport through the network; a plurality of nodes connected in sequence to the optical fiber, each node comprising: an optical input port for receiving optical signals from the optical fiber comprising wavelength channels; one or more modulators coupled to the optical input port wherein each modulator is configured to modulate a respective first wavelength channel of the wavelength channels with respective data to produce a modulated first wavelength channel; and an optical output port configured to transmit a combination of the one or more modulated first wavelength channels with a subset of the wavelength channels on the optical fiber.

Optionally, in any of the preceding embodiments, the optical network further comprising: one or more receivers coupled to the optical input port through an optical power splitter wherein each receiver is configured to receive a portion of optical power of the wavelength channels.

Optionally, in any of the preceding embodiments, the optical network wherein a first node of the plurality of nodes is configured to demultiplex received wavelength channels, split a portion of optical power from each of the received wavelength channels to a respective receiver, send each of the received wavelength channels through one of the modulators, multiplex one or more of the received wavelength channels with one or more modulated wavelength channels to form the combined optical signal and transmit the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.

Optionally, in any of the preceding embodiments, the optical network wherein each of the plurality of the nodes is not equipped with the laser bank.

Optionally, in any of the preceding embodiments, the optical network wherein each modulator of the one or more modulators has a transmitting state and a bypassing state and wherein an input signal to a modulator is not modulated when the modulator is in the bypassing state.

Optionally, in any of the preceding embodiments, the optical network wherein one of the respective first wavelength channels passes through a first modulator and a second modulator, and wherein the first and second modulators are located in separate nodes of the plurality of nodes in one of the DWDM buses.

Optionally, in any of the preceding embodiments, the optical network wherein only one of the first and second modulators is in the transmitting state at any given time, and the other of the first and second modulators is in the bypassing state at the given time.

Optionally, in any of the preceding embodiments, the optical network wherein one or more optical amplifiers are configured between two of the plurality of nodes or between the laser bank and a first of the plurality of nodes.

Optionally, in any of the preceding embodiments, the optical network wherein a first node of the plurality of nodes comprises a plurality of photonic circuits coupled to the optical fiber, wherein the plurality of photonic circuits are configured to split an input light from the optical source into two polarizations in separate waveguides, and process the two polarizations of the input light by two identical photonic circuits of the plurality of photonic circuits to generate desired modulation patterns for transmission of the optical signal in the network.

Optionally, in any of the preceding embodiments, the optical network wherein a first node of the plurality of nodes comprises a photonic circuit coupled to the optical fiber, wherein the photonic circuit is configured to be with active feedback to track a polarization of an input light from the optical source and to maintain the polarization to a desired direction.

Optionally, in any of the preceding embodiments, the optical network wherein an output from the photonic circuit is configured to be fed into a single modulator of the one or more modulators to generate desired modulation for transmission in the network.

Another embodiment includes a method for communication in a dense wavelength-division multiplexing (DWDM) optical network, the method comprising: generating, by a laser bank, a plurality of unmodulated optical signals each having a different wavelength channel; multiplexing the unmodulated optical signals to produce a combined, unmodulated optical signal; transmitting the combined, unmodulated optical signal through an optical fiber for transport through the optical network to a plurality of nodes that are connected in sequence to the output of the optical multiplexer; receiving, by each of the plurality of nodes, the unmodulated optical signal from the optical fiber comprising wavelength channels; modulating, by each the plurality of nodes, a respective first wavelength channel of the wavelength channels with respective data to produce a modulated first wavelength channel; and transmitting, by each the plurality of nodes, a combination of the respective modulated first wavelength channel with a subset of the wavelength channels on the optical fiber.

Optionally, in any of the preceding embodiments, the method further comprising demultiplexing the subset of wavelength channels, by a first node of the plurality of nodes; splitting, by the first node, a portion of optical power from each of the subset of the wavelength channels to a receiver; sending, by the first node, each of the subset of the wavelength channels through one or more modulators to produce modulated second wavelength channels; multiplexing, by the first node, the modulated second wavelength channels to form the combined optical signal; and transmitting, by the first node, the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.

Optionally, in any of the preceding embodiments, the method wherein each modulator of the one or more modulators has a transmitting state and a bypassing state and wherein an input signal to a modulator is not modulated when the modulator is in the bypassing state.

Optionally, in any of the preceding embodiments, the method wherein one of the respective first wavelength channels of the passes through a first modulator and a second modulator, and wherein the first and second modulators are located in separate nodes of the plurality of nodes in one direction of the optical signals transmission in the network.

Optionally, in any of the preceding embodiments, the method wherein only one of the first and second modulators is in the transmitting state at any given time, and the other of the first and second modulators is in the bypassing state at the given time.

Another embodiment includes an optical network node connected in sequence to an optical fiber of an optical network deployed a dense wavelength-division multiplexing (DWDM) communication, comprising: an optical input port configured to receive unmodulated optical signals from the optical fiber comprising wavelength channels; one or more modulators coupled to the optical input port wherein each modulator is configured to modulate a respective first wavelength channel of the wavelength channels with respective data to produce a modulated first wavelength channel; one or more receivers coupled to the optical input port through an optical power splitter wherein each receiver is configured to receive a portion of optical power of the respective first wavelength channel of the wavelength channels; and an optical output port configured to transmit a combination of the one or more modulated first wavelength channels with a subset of the wavelength channels on the optical fiber.

Optionally, in any of the preceding embodiments, the optical network node wherein the optical network node further comprises a demultiplexer to demultiplex all wavelength channels, split the portion of the optical power from each of a subset of the wavelength channels to the one or more receivers, send each of a subset of the wavelength channels through a modulator, multiplex all the wavelength to form the combined optical signal and transmit the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.

Optionally, in any of the preceding embodiments, the optical network node wherein each modulator of the one or more modulators has a transmitting state and a bypassing state and wherein an input signal to a modulator is not modulated when the modulator is in the bypassing state.

Optionally, in any of the preceding embodiments, the optical network node wherein one of the respective first wavelength channels passes through a first modulator and a second modulator, and wherein the first and second modulators are located in separate nodes of the plurality of nodes in one direction of the optical signals transmission in the network.

Optionally, in any of the preceding embodiments, the optical network node wherein only one of the first and second modulators is in the transmitting state at any given time, and the other of the first and second modulators is in the bypassing state at the given time.

Optionally, in any of the preceding embodiments, the optical network node wherein one or more optical amplifiers are configured between two of the plurality of nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

FIG. 1 is a schematic diagram of a conventional DWDM optical network system.

FIG. 2 is a schematic diagram of an example of DWDM optical signal transmitting portion in conventional DWDM optical network system.

FIG. 3 is a schematic diagram of a DWDM optical network optically sourced by a centralized laser bank according to an embodiment of the disclosure.

FIG. 4 is schematic diagram of a DWDM optical network optically sourced by a centralized laser bank according to another embodiment of the disclosure.

FIG. 5 illustrates a dynamic link switching scenario in a DWDM optical network according to an embodiment of the disclosure.

FIG. 6 illustrates a dynamic link switching scenario in a DWDM network according to another embodiment of the disclosure.

FIG. 7 illustrates a dynamic link switching scenario in a DWDM network according to another embodiment of the disclosure.

FIG. 8 is schematic diagram of a DWDM optical network optically sourced by a centralized laser bank according to an embodiment of the disclosure.

FIG. 9 illustrates a dynamic link switching scenario in a DWDM network according to another embodiment of the disclosure.

FIG. 10 illustrates a polarization diversity approach according to an embodiment of the disclosure.

FIG. 11 illustrates a polarization diversity approach according to another embodiment of the disclosure.

FIG. 12 is a schematic diagram illustrating a photonic processor according to an embodiment of the disclosure.

FIG. 13 is a flowchart of a method of transmission in a DWDM network according to an embodiment of the disclosure.

FIG. 14 is a schematic diagram of a network device according to an embodiment of the disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that, although illustrative implementations of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

FIG. 1 is a schematic diagram of a conventional DWDM optical network system. The DWDM optical system 100 includes a plurality of nodes 110, 120, 130. Messages are transmitted from a node to another. A DWDM optical signal transmitting portion is shown for the node 120 as an example. Optical signals at some wavelengths carry data from other nodes are dropped to the receivers (RX) 107, 109 of the node 120; the receivers 107, 109 convert the optical signal to an electronic signal. CW optical waves from lasers 106, 108 are modulated at the modulators 102, 104 to carry the data from the node 120; the modulators 102, 104 converts an optical signal to an electronic signal by changing the amplitude or phase or both of the amplitude and phase of the CW optical waves according to the electronic signal. The data are added to the DWDM optical link through the wavelength multiplexer for transporting. An amplifier 115 is coupled between node 110 and node 120. An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal.

FIG. 2 is a schematic diagram of an example of DWDM optical signal transmitting portion in conventional DWDM optical network system. The DWDM optical system 220 includes an array of optical line-cards 201 coupled to an optical MUX card 203 via a plurality of patchcords 230. Each optical line-card 201 comprises a CW laser 210 and an optical modulator 220. The output port of the CW laser 201 is coupled to the input port of the optical modulator 220. The CW lasers 201 may be distributed feedback (DFB) lasers or any type of lasers. The CW lasers 210 function as CW optical sources to generate optical signals. The CW laser 201 may be employed with or without a wavelength locker. Each CW laser 201 is configured to transmit at a different wavelength. The output port of each CW laser 210 may be coupled to any suitable optical device for optical signal processing such as monitoring, modulation, photo detection, and digital signal processing (DSP). The optical modulator 220 may be a Mach-Zehnder (MZ) modulator, an electro-absorption modulator, a directly modulated laser (DML) modulator, or the like. Optical modulators 220 may control the optical signals by modulating the amplitude and/or phase of the optical signals. Each line-card 201 may further comprise an optical tap and a photodetector (PD) for monitoring optical power and a DSP chip for additional optical signal processing. The patchcords 230 are optical cables suitable for optically connecting optical devices such as the optical line-cards 201 and the optical MUX card 203. The optical MUX card 203 comprises an optical MUX 205, which may be an optical combiner, waveguides, or an arrayed waveguide grating (AWG) configured to multiplex all wavelengths transmitted by the optical line-cards 201 into one single fiber for optical transport. The multiplexed optical signal may be sent to another optical network. The CW lasers 210 and the other optical signal processing functions such as modulators 220, line cards 230 are an integral part.

For example, a DWDM optical system with 80 wavelength channels where the system 200 may be referred to as an 80-wavelength DWDM optical system. The system 200 comprises 80 optical line-cards 201 stacked together for transmitting 80 different high-speed modulated optical signals assuming each optical line-card 201 transmits at one individual wavelength. In addition, the system 200 comprises 80 individual single-mode optical patchcords 230 each optically connecting an output port of an optical line-card 201 to an input port of the optical MUX card 203. As such, the system 200 constrains and limits the system physical size, system cost, power consumption, and fiber management.

DWDM optical communication systems carry multiple optical signal channels, each channel being assigned a different wavelength. Optical signal channels are generated, multiplexed to form an optical signal comprised of the individual optical signal channels, and transmitted over a single waveguide such as an optical fiber. The optical signal is subsequently demultiplexed such that each individual channel can be routed to a designated receiver.

In an embodiment, an optical bus configured for a dense wavelength-division multiplexing (DWDM) network, the optical bus comprises an optical source configured to generate a plurality of unmodulated optical signals each having a different wavelength; an optical multiplexer configured to multiplex the unmodulated optical signals to produce a combined, unmodulated optical signal, and to transmit the combined, unmodulated optical signal through an optical fiber; a plurality of nodes connected in sequence to the output of the optical multiplexer.

Furthermore, each of the plurality of the nodes are not equipped with the optical source.

Furthermore, each of the plurality of the nodes is equipped with a plurality of optical receivers each detecting the optical signal after the wavelength of the optical signal is de-multiplexed and optical power of the optical signal is split.

Disclosed herein are various embodiments of a DWDM network that uses one centralized laser bank to optically power or optically source the entire network, allowing the network nodes to operate without costly lasers. The disclosed embodiments provide benefits such as simplicity, compactness, high scalability, high reliability, reduced system cost, lower power consumption, simple fiber management, and enabling building of fully intelligent optical networks. The disclosed embodiments are suitable for use in metropolitan networks covering distances from about 100 kilometer (km) to about 1000 km.

In an embodiment, a DWDM network comprises a headend node supplying a centralized DWDM optical source to a number of nodes logically arranged in a ring shape. The number of nodes may be about 2 to about 20. Unlike conventional optical networks employing DWDM system such as the system 100, no laser source is needed at the nodes. All nodes draw optical signals from the centralized source in the headend node, modulate the optical signal, and send the modulated optical signal back into the network. Without having an optical source at each node, the nodes may be built with large-scale integration, high yield, and low cost on silicon photonics platforms. In addition, all nodes may be identical, operating as white boxes without physical wavelength assignments, which significantly simplifies network implementation and supply chain management. White boxes refer to the network nodes that do not include any wavelength-specific component. Further, each node may be dynamically configured to modulate and/or receive any wavelength of the centralized DWDM optical source. Thus, the disclosed embodiments allow for dynamic network reconfiguration without changing physical positions and/or connections of the nodes.

FIG. 3 is a schematic diagram of a DWDM optical network optically sourced by a centralized laser bank according to an embodiment of the disclosure. The DWDM network 300 is formed by two or more optical fibers that sequentially connect all the nodes 310, 320, 330 in the network 300. For example, optical signals in a network of two optical fibers propagate in opposite directions. A CW optical source circuit pack 301 functions as a CW optical source for an array of DWDM wavelengths with a single optical output port. The CW optical source circuit pack 301 comprises one or more laser banks 301 which generate a plurality of optical signals for the network. Unlike the DWDM systems 100, 200, the laser bank 301 provides optical source power for the entire network 300 instead of having optical sources at individual nodes such as nodes 310, 320, 330. The laser bank 301 is configured to provide an array of DWDM wavelengths of interest in a CW mode to cover all DWDM wavelengths of interest in the network 300. The laser bank 301 may send optical signals comprising the array of DWDM wavelengths into network 300 via a single optical output port. One or more optical amplifiers 315 may be configured between two of the plurality of nodes 310, 320, 330 or between the CW optical source circuit pack 301 and a first of the plurality of nodes 310, 320, 330. Optical amplifiers may use a doped optical fibre as a gain medium to amplify an optical signal. They may be related to fibre lasers. The signal to be amplified and a pump laser are multiplexed into the doped fibre, and the signal is amplified through interaction with the doping ions. The most common example of optical amplier is an Erbium Doped Fibre Amplifier (EDFA). The EDFA is an optical amplifier that uses a waveguide to boost an optical signal.

A DWDM optical signal transmitting portion is shown for the node 320 as an example. Optical signals at some wavelengths carry data from other nodes are dropped to the receivers (RX) 321, 323, 325, 327. The receivers 321, 323, 325, 327 may convert the optical signal to an electronic signal. Optical signals at some wavelengths carry data from other nodes are sent to modulators 322, 324, 326, 328. Instead of receiving optical signals from a laser at the node 320 itself, modulators 322, 324, 326, 328 may receive optical signal from another node directly. A demultiplexer (DEMUX) 305 demultiplexes optical signals from a node that is connected to the node 320, and the optical signals are sent to the modulators 322, 324, 326, 328 for modulation, where the modulators 322, 324, 326, 328 convert an optical signal to an electronic signal by changing the amplitude or phase or both of the amplitude and phase of the optical signal according to the electronic signal. The data are added to the DWDM optical link through the wavelength multiplexer (MUX) 307 for transporting.

The precision of the DWDM wavelength may be achieved through optical wavelength lockers. For example, an individual wavelength locker may be employed to lock each wavelength separately. Alternatively, a common wavelength locker may be employed to lock all wavelengths. An example wavelength locker may be an Etalon-based wavelength locker. With advanced photonic integration technologies, the arrays of CW lasers 301 with DWDM wavelengths and the optical MUX 303 may be integrated into a single photonic chip with or without an on-chip wavelength locker. For example, when employing the CW optical source circuit pack 300 in an 80-wavelength DWDM optical system similar to the network 200, the CW optical source circuit pack 300 may comprise a photonic chip comprising 80 CW lasers such as the CW lasers 301 with DWDM wavelengths of interest integrated with an optical MUX such as the optical MUX 303 through photonic integration technologies. In some embodiments, the photonic chip may further integrate wavelength lockers onto the chip. Thus, a single CW optical source circuit pack 300 may provide 80 CW DWDM wavelengths and output the 80 CW DWDM wavelengths through a single optical output port. The optical MUX 303 may be of AWG-type, MZ-type, or micro-rings based on silicon photonic technology.

The plurality of nodes 310, 320, 330 may receive optical signals from a node that is connected subsequently or from any node that is connected in the network.

The architecture of the CW optical source circuit pack 300 provides several benefits. For example, a common wavelength locker may be used for all wavelengths instead of a separate wavelength locker at each node such as the nodes 310, 320, 330, and thus reduces cost. The wavelength locking precision may be high due to less variation from locker to locker. The integrated architecture allows for tight spacing, high reliability, and high scalability, where the numbers of lasers may be selected as needed. In addition, a common thermal-electric cooler (TEC) may be used for all wavelengths instead of a separate TEC at each node, and thus further reduces cost. In addition, the use of a common TEC lowers power consumption and achieves a higher efficiency. The major benefit is the sharing of a single source among multiple network nodes. Thus, the system cost may be greatly reduced.

FIG. 4 is schematic diagram of a DWDM optical network optically sourced by a centralized laser bank according to another embodiment of the disclosure. All elements described in the DWDM network 400 can be formulated into the DWDM network 300. An example of DWDM optical signal transmitting portion for nodes 420 and 440 of the DWDM network 400 is shown. Each of the nodes 420, 440 are not equipped with laser bank. Thus nodes 420, 440 get their optical source only from the centralized laser bank 401. A first node 420 of the plurality of nodes may be configured to demultiplex the wavelength channels, split a portion of optical power λ1, λn from each of the subset of the wavelength channels to a respective receiver 421, 423, send each of the subset of the wavelength channels through the one or more modulators 424, 428, multiplex all the received wavelength channels to form the combined optical signal and transmit the combined signal to other nodes 410, 440, 460 of the plurality of nodes in sequence on the network simultaneously. Each modulator 424, 428, 424′, 428′ of the one or more modulators may have a transmitting state and a bypassing state. A respective first wavelength channel of the wavelength channels may pass through at least two of the modulators 424, 428, 424′, 428′ and wherein the at least two of the modulators 424, 428, 424′, 428′are located in separate nodes of the plurality of nodes 420, 440 at one direction of the optical signals transmission in the network 400. Among the at least two of the modulators 424, 428, 424′, 428′ that a wavelength channel passes through, only one of them may be at the transmitting state at any given time, the rest of the at least two of the modulators 424, 428, 424′, 428′ may be at the bypassing state, and wherein the respective first wavelength channel of the wavelength channels passes through the rest of the at least two of the modulators 424, 428, 424′, 428′ unaltered. One or more optical amplifiers 415 may be configured between two of the plurality of nodes 410, 420, 430 or between a CW optical source circuit pack e.g. laser bank 401 and a first of the plurality of nodes 410, 420, 430. The most common example of optical amplier is an Erbium Doped Fibre Amplifier (EDFA). The EDFA is an optical amplifier that uses a waveguide to boost an optical signal.

In an embodiment, a DWDM network comprises at least two counter-propagating DWDM buses, each of which comprises a laser bank configured to generate a plurality of unmodulated optical signals each having a different wavelength channel, an optical multiplexer configured to multiplex the unmodulated optical signals to produce a combined and unmodulated optical signal; and to transmit the combined, unmodulated optical signal through an optical fiber for transport through the network. The DWDM network may also comprises a plurality of nodes connected in sequence to the optical fiber, each node comprises an optical input port for receiving optical signals from the optical fiber comprising wavelength channels; one or more modulators coupled to the optical input port wherein each modulator is configured to modulate a respective first wavelength channel of the wavelength channels with respective data; and an optical output port configured to transmit a combination of the modulated first wavelength channel with a subset of the wavelength channels on the optical fiber.

In addition, one or more receivers coupled to the optical input port through an optical power splitter wherein each receiver may be configured to receive a portion of optical power of the wavelength channels.

In addition, a first node of the plurality of nodes may be configured to demultiplex the wavelength channels, split a portion of optical power from each of the subset of the wavelength channels to a receiver, send each of the subset of the wavelength channels through the one or more modulators, multiplex all the received wavelength channels to form the combined optical signal and transmit the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.

In addition, each of the plurality of the nodes may be not equipped with the laser bank.

In addition, each modulator of the one or more modulators may have a transmitting state and a bypassing state.

In addition, the respective first wavelength channel of the wavelength channels may pass through at least two of the modulators, and wherein the at least two of the modulators are located in separate nodes of the plurality of nodes at one direction of the optical signals transmission in the network.

In addition, among the at least two of the modulators that a wavelength channel passes through, only one of them may be at the transmitting state at any given time, the rest of the at least two of the modulators may be at the bypassing state, and wherein the respective first wavelength channel of the wavelength channels passes through the rest of the at least two of the modulators unaltered.

In addition, one or more optical amplifiers may be configured between two of the plurality of nodes or between the laser bank and a first of the plurality of nodes.

In addition, a first node of the plurality of nodes may comprise a plurality of photonic circuits coupled to the optical fiber, wherein the plurality of photonic circuits may be configured to split an input light from the optical source into two polarizations in separate waveguides, and process the two polarizations of the input light by two identical photonic circuits of the plurality of photonic circuits to generate desired modulation patterns for transmission of the optical signal in the network.

In addition, a first node of the plurality of nodes may comprise a photonic circuit coupled to the optical fiber, wherein the photonic circuit may be configured to be with active feedback to track a polarization of an input light from the optical source and to maintain the polarization to a desired direction.

In addition, an output from the photonic circuit may be configured to be fed into a single modulator of the one or more modulators to generate desired modulation for transmission in the network.

In an embodiment, an optical network node connected in sequence to an optical fiber of an optical network deployed a dense wavelength-division multiplexing (DWDM) communication as described in above various embodiments may comprise: an optical input port configured to receive unmodulated optical signals from the optical fiber comprising wavelength channels; one or more modulators coupled to the optical input port wherein each modulator is configured to modulate a respective first wavelength channel of the wavelength channels with respective data; one or more receivers coupled to the optical input port through an optical power splitter wherein each receiver is configured to receive a portion of optical power of the respective first wavelength channel of the wavelength channels; and an optical output port configured to transmit a combination of the one or more modulated first wavelength channels with a subset of the wavelength channels on the optical fiber.

In addition, the optical network node may further comprise a demultiplexer to demultiplex all wavelength channels, split the portion of the optical power from each of a subset of the wavelength channels to the one or more receivers, send each of a subset of the wavelength channels through a modulator, multiplex all the wavelength to form the combined optical signal and transmit the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.

In addition, the optical network node may further comprise that each modulator of the one or more modulators has a transmitting state and a bypassing state.

In addition, the optical network node may further comprise that the respective first wavelength channel of the wavelength channels passes through at least two of the one or more modulators, and wherein the at least two of the modulators are located in separate nodes of the plurality of nodes at one direction of the optical signals transmission in the network.

In addition, the optical network node may further comprise that among the at least two of the modulators, only one of them is at the transmitting state at any given time, the rest of the at least two of the modulators are at the bypassing state, and wherein the respective first wavelength channel of the wavelength channels passes through the rest of the at least two of the modulators unaltered.

In addition, the optical network node may further comprise that one or more optical amplifiers are configured between two of the plurality of nodes.

The optical network node may be configured to carry out the methods as described above in various embodiments.

FIG. 5 illustrates a dynamic link switching scenario in a DWDM optical network according to an embodiment of the disclosure. The DWDM network is such as the networks 300 and 400 according to an embodiment of the disclosure. The scenario 500 illustrates a headnode 510, a headnode 520, connected with a node X 530 which is similar to the nodes 310, 320, 330, 410, 420, 430, 440 and 460 dynamically switches links to downstream nodes Y 540, Z 550, 560, 570. The laser bank 301, 401 is located at the headend nodes 510, 520 respectively.

The optical signals transmitted by the headnode 510, 520 may be amplified at every node 530, 540, 550, 560, 570 until terminated at the RX of a node 530, 540, 550, 560, 570 or by the end of the fiber 520. The nodes 530, 540, 550, 560, 570 on the ring may not have any laser source, but may instead have amplifiers as described more fully below. Thus, all of the nodes 530, 540, 550, 560, 570 may be identical. Each node 530, 540, 550, 560, 570 is capable of choosing any wavelength to encode data to be detected by subsequent nodes 530, 540, 550, 560, 570 of choice, as described more fully below. The network 500 may operate as a mesh network.

While the physical topology of the network 500 may be fixed, the logical topology of the network 500 is determined by the wavelength assignments. Thus, the logical connections of the network 500 may be dynamically reconfigured by adjusting the wavelength assignments. It should be noted that the geographical locations of the nodes in the network 500 are not required to be arranged in a circle as shown in FIG. 5.

As shown, at a first time the node X 530 routes data traffic P 533, for example, from a tributary interface such as the tributary interface 531 of the node X 530 to a node Y 540 and another data traffic Q 535 from the node X 530 to a node Z 550. The node X 530 may dynamically reroute the data traffic P 533 and the data traffic Q 535 by activating a modulator corresponding to the specific wavelength for network node Z 550 or the network node Y 540.

In an embodiment, the network 500 is a metropolitan network. In such an embodiment, the distance between the neighboring nodes are typically in the range of a few kilometers (km) to tens of km while the total length of the ring-shaped network 500 may range from about 100 km to about 1000 km. The network 500 is suitable for traffic patterns that require any node to any node connections, for example, a mesh network, and head to satellite node connections with dynamic link provisioning capability.

FIG. 6 illustrates a dynamic link switching scenario in a DWDM network according to another embodiment of the disclosure. The DWDM network is such as the networks 300 and 400. The scenario 500 may be carried out like the scenario 600. A headnode 610 is illustrated which is connected with a node X 620 which is similar to the nodes 310, 320, 330, 410, 420, 430, 440 and 460 dynamically switches links to downstream nodes 620, 630, 640, 650, 660, 620′, 630′, 640′, 650′, 660′. As shown, at a first time the node 620 routes data traffic P 623, for example, from a tributary interface such as the tributary interface 621 of the node 620 to a node 630 and another data traffic Q 625 from the node 620 to a node 640. The node 620 may dynamically reroute the data traffic P 623 and the data traffic Q 625 by activating a modulator corresponding to the specific wavelength for network node 640 or the network node 630. Another example of using dynamic link switching in a network 600 is for multicast and/or broadcast. The data traffic from the starting node (network node 620) can be provisioned to multi-casting and/or broadcasting to partial/all of the downstream nodes at time T₀+δT per network needs. This may be achieved by activating all the modulators of the wavelengths for the downstream nodes relative to the network node 620. At time T₀, it was routed to network node 630 by activating the modulators for the specific wavelengths to drop off at network node 630.

FIG. 7 illustrates a dynamic link switching scenario in a DWDM network according to another embodiment of the disclosure. The DWDM network is such as the networks 300, 400, 500, 600. The scenario 700 corresponds to the scenario 600 and provides a more detailed view of data paths of the data traffic P and the data traffic Q. As shown, At time T₀, the node 720 routes the data traffic P from a client interface 724 of the node 720 via a cross connect 725 of the node 720 to a client data interface 734 of the node 730 via a cross connect 735 of the node 730. The node 720 routes the data traffic Q from a client interface 722 of the node 720 via the cross connect 725 of the node 720 to a client data interface 744 of the node 740 via a cross connect 745 of the node 740.

At time T₀+δT, the node 720′ routes the data traffic Q from the client interface 722′ of the node 720 via the cross connect 725′ of the node 720 to a client data interface 735′ of the node 730 via the cross connect 735′ of the node 730′. The node 720′ routes the data traffic P from the client interface 724′ of the node 720′ via the cross connect 725′ of the node 720 to the client data interface 744′ of the node 740′ via the cross connect 745′ of the node 740′.

FIG. 8 is a schematic diagram of a DWDM optical network optically sourced by a centralized laser bank according to an embodiment of the disclosure. All elements described in the DWDM network 800 can be formulated into the DWDM networks 300, 400. An example of DWDM optical signal transmitting portion for node 810, 820, 830 of the DWDM network 800 is shown. A switch for modulator 803 is equipped with the node 820. When the switch is on, the modulator 803 modulates on the optical signal that passes, when the switch if off, the modulator 803 does not add data on the optical signal so that the optical signal simple passes through the modulator 803 without being altered. In other saying, the optical signal passes through the modulator 803 unaltered. One or more optical amplifiers 815 may be configured between two of the plurality of nodes 810, 820, 830. An example of optical amplier is an Erbium Doped Fibre Amplifier (EDFA). The EDFA is an optical amplifier that uses a waveguide to boost an optical signal.

FIG. 9 illustrates a dynamic link switching scenario in a DWDM network according to another embodiment of the disclosure. The DWDM network is for example the networks 300, 400, 500, 600, 700 and 800. The scenario 900 corresponds to the scenario 700 and provides a view of data paths of the data traffic. As shown, at time T₀, the node 920 routes the data traffic Q from a client interface 922 of the node 920 via a cross connect 925 of the node 920 to a client data interface 932 of the node 930 via a cross connect 935 of the node 930. At time T₀+δT, the node 920′ routes the data traffic Q from the client interface 922′ of the node 920′ via the cross connect 925′ of the node 920′ to client data interfaces 932′, 942′ of all nodes via corresponding cross connects 935′, 945′. It should be noted that although the scenarios 700, 900 illustrate dynamic downstream link switching between different times, the network may perform downstream link swtiching as often as needed.

Another advantage of the disclosed centralized laser bank network architecture when compared to traditional DWDM network such as the systems 100, 200 is that the disclosed network architecture (e.g., the networks 300, 400, 500, 600, 700, 800 and 900) eliminates a large number of lasers such as the CW lasers which are otherwise required by each node in the systems 100, 200 to implement wavelength switch capabilities. For an example, a network with N wavelengths and M nodes, the saving may be about 2×N×(M−1) lasers. If N=40 and M=6, the network requires about 400 lasers.

One assumption associated with the disclosed centralized laser bank network architecture is the capability of arbitrary polarization tracking at each node. Polarization of light may rotate randomly in ordinary single-mode fiber (SMF), the input polarization state at each node may be a random combination of transverse electric (TE) and transverse magnetic (TM) modes. Since TE and TM modes behave differently in most photonic circuits, processing of both TE and TM modes in one circuit may be difficult.

FIG. 10 illustrates a polarization diversity approach according to an embodiment of the disclosure. The approach 1000 may be employed by the nodes in systems 300, 400, 500, and 600 when processing light signals. In the approach 1000, an integrated photonic processor 1020 comprises two waveguides positioned between two polarization splitter-rotators (PSRs) 1021 and 1021′. Each of the waveguides 1025, 1027 is coupled to an identical photonic circuit 1023 and 1023′, which may correspond to a transmitter, a modulator such as the MODs 322, 324, 326, 328, 424, 428 etc. As described in above embodiments, or a RX such as the RXs 321, 323, 325, 327, 421, 423, etc. As described in above embodiments. The PSR 1021 is coupled to a CW optical source 1010 similar to the CW laser 302 and 401, which may be part of a laser bank or the CW optical source circuit pack 301. The PSR 1021 receives an incoming light signal comprising TE and TM modes from the CW source 1010. The PSR 1021 splits the light signal into two portions and rotate the two portions into the same polarization mode, for example, the TE mode. The PSR 1021 passes one portion to the waveguide and the other portion to the waveguide 1025. Each photonic circuit 1023, 1023′ processes one of the light portions. After processing, the processed light from one of the waveguides 1025 and 1027 is rotated back to the orthogonal polarization, for example, the TM mode. The PSR 1021, 1021′ combined the outputs of the waveguides 1025 and 1027 such that no coherent interference is present between the two outputs.

FIG. 11 illustrates a polarization diversity approach according to another embodiment of the disclosure. The approach 1100 may be employed by the nodes in the networks described above 300, 400, 500, 600, 700, 800 and 900 when processing light signals from a network. The approach 1100 may not require to have two copies of the same photonic circuit. The approach 1100 comprises a PSR 1110, a plurality of couplers 1122, 1124, 1126, a plurality of phase shifters (PSs) 1121, 1123, 1125, and two waveguides 1140 and 1150. The PSR 1110 is similar to the PSRs in FIG. 10. The waveguides 1140 and 1150, the couplers 1122, 1124, 1126 and the PSs 1121, 1123, 1125, form multiple stages of Mach-Zehnder interferometers (MZIs) 1160. The PSs 1121, 1123, 1125 are configured to phase-shift the light signal propagating along the waveguide 1140, 1150. The PSR 1110 splits an incoming light signal comprising a combination of TE and TM modes, for example, received from an input fiber, into two portions and rotates the two portions into the same polarization. The PSR 1110 passes one portion to the waveguide 1140 and another portion to the waveguide 1150. The light signals of the waveguides 1140 and 1150 are coherently combined into one output signal. However, the two polarization eigenmodes, TE and TM, in the input fiber have random amplitude and phase relationships between them. Thus, the MZIs 1160 are configured such that light signals propagating along the two waveguides 1140 and 1150 constructively interfered with each other with a minimal loss when the light signals are combined. The PSs 1121, 1123, 1125 actively adjusts phase delays between the two waveguides 1140 and 1150 to track the time evolution of the polarization state in the input fiber. The approach 1100 may not need to have two copies of the same photonic circuit as in the approach 1000. Thus, the approach 1100 may save even more power and area and reduce complexity.

FIG. 12 is a schematic diagram illustrating a photonic processor according to an embodiment of the disclosure. The photonic processor 1200 may be employed by the nodes in the networks 300, 400, 500, 600, 700, 800 and 900. The photonic processor 1200 comprises an integrated N-channel electrical switch 1220, which enables the provision of dynamic links to downstream nodes through different wavelengths. The photonic processor 700 comprises a tributary interface 1210, the N-channel electrical switch 1220, a modulator array 1240, a MUX 1250, and an ebrium-doped filter amplifier (EDFA) 1260. The N-xhannel electrical switch 1220 is positioned between the tributary interface 710 and the modulator array 1240. The modulator array 1240 is coupled to a DWDM laser bank 1230 similar to the laser bank described in above embodiments and the CW optical source circuit pack 300. The MUX 1250 is similar to the MUX described in above embodiments. The EDFA 1260 is similar to the OAs 315 and 415 and is coupled to the MUX 1250.

The tributary interface 1210 is configured to interface a plurality of client data interfaces. The modulator array 1240 comprises a plurality of modulators similar to the optical modulators described in above embodiments. The N-Channel eletrical switch 1220 is also referred to as a cross connect. The N-channel electrical switch 1220 is configured to control the activation of the modulators in the modulator array 1240 and interconnects the client data interface to corresponding modulators, for example, based on network requests. Thus, the modulators in the modulator array 1240 may modulate client data onto light generated by the DWDM laser bank 1230 according to the configuration set by the N-channel electrical switch 1220. The photonic processor 1200 may further be integrated with RXs similar to RXs described in above embodiments.

FIG. 13 a flowchart of a method of transmission in a DWDM network according to an embodiment of the disclosure. Various embodiments of the method may be carried out in network systems 300, 400, 500, 600, 700, 800, 900 as described above. In an embodiment, a method for communication in a dense wavelength-division multiplexing (DWDM) optical network adapted to the various embodiments of above described DWDM optical network, at step 1310 the method may comprise a laser bank generating a plurality of unmodulated optical signals each having a different wavelength channel; at step 1320, multiplexing the unmodulated optical signals to produce a combined, unmodulated optical signal; at step 1330, transmitting the combined, unmodulated optical signal through an optical fiber for transport through the optical network to a plurality of nodes that are connected in sequence to the output of the optical multiplexer receiving, at step 1340, by the plurality of nodes, the unmodulated optical signal from the optical fiber comprising wavelength channels; at step 1350, modulating a respective first wavelength channel of the wavelength channels with respective data; and at step 1360, transmitting a combination of the one or more modulated first wavelength channels with a subset of the wavelength channels on the optical fiber.

In addition, the method may further comprise demultiplexing the wavelength channels, by a first node of the plurality of nodes; at step 1370, splitting a portion of optical power from each of the subset of the wavelength channels to a receiver; sending each of the subset of the wavelength channels through one or more modulators which does the modulating; multiplexing the wavelength channels to form the combined optical signal; and transmitting the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.

In addition, step 1350 may further comprises at step 1380 the plurality of nodes receiving the unmodulated optical signal from the optical fiber comprising wavelength channels; modulating a respective first wavelength channel of the wavelength channels with respective data; and transmitting a combination of the first respective wavelength channel with a subset of the wavelength channels on the optical fiber.

In addition, the method may further comprise that each modulator of the one or more modulators has a transmitting state and a bypassing state.

In addition, at step 1390, the method may further comprise that the respective first wavelength channel of the wavelength channels passes through at least two of the one or more modulators, and wherein the at least two of the modulators are located in separate nodes of the plurality of nodes at one direction of the optical signals transmission in the network.

In addition, at step 1395, the method may further comprise that among the at least two of the modulators, only one of them is at the transmitting state at any given time, the rest of the at least two of the modulators are at the bypassing state, and wherein the respective first wavelength channel of the wavelength channels passes through the rest of the at least two of the modulators unaltered.

FIG. 14 is a schematic diagram of a network device according to an embodiment of the disclosure. The device 1400 is suitable for implementing the disclosed embodiments described above. The device 1400 may function as a headend node such as the headend node in networks 300, 400, 500, 600, 700, a laser bank such as the laser bank 302, 401 and the CW optical source circuit pack 301, or a network node such as the network nodes 310, 320, 330, 410, 420, 430 in a DWDM network. The device 1400 comprises ingress ports 1410 and receiver units (Rx) 1420 for receiving data; a processor, logic unit, or central processing unit (CPU) 1430 to process the data; transmitter units (Tx) 1440 and egress ports 1450 for transmitting the data; and a memory 1460 for storing the data. The device 1400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports 1410, the receiver units 1420, the transmitter units 1440, and the egress ports 1450 for egress or ingress of optical or electrical signals.

The processor 1430 is implemented by any suitable combination of hardware, middleware, firmware, and software. The processor 1430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors. The processor 1430 is in communication with the ingress ports 1410, receiver units 1420, transmitter units 1440, egress ports 1450, and memory 1460. The processor 1430 comprises a DWDM processing component 1470. The DWDM processing component 1470 implements the various disclosed embodiments described above. The inclusion of the DWDM processing component 1470 therefore provides a substantial improvement to the functionality of the network and effects a transformation of the network to a different state. Alternatively, the DWDM processing component 1470 is implemented as instructions stored in the memory 1460 and executed by the processor 1430. The processor 1730 may have a transmitting state and a bypassing state. A respective first wavelength channel of the wavelength channels may pass through at the bypassing state with the optical signal unaltered. A respective first wavelength channel of the wavelength channels may be modulated with data at the transmitting state.

The memory 1460 comprises one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 1460 may be volatile and non-volatile and may be read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), and static random-access memory (SRAM).

The memory 1460 comprises computer-readable non-transitory media. The computer-readable non-transitory media includes all types of computer readable media, including magnetic storage media, optical storage media, flash media and solid state storage media.

It should be understood that software can be installed in and sold with the network device 1400. Alternatively the software can be obtained and loaded into the network device 1400, including obtaining the software through physical medium or distribution system, including, for example, from a server owned by the software creator or from a server not owned but used by the software creator. The software can be stored on a server for distribution over the Internet, for example.

The use of the term “about” means a range including ±10% of the subsequent number, unless otherwise stated. While several embodiments have been provided in the present disclosure, it may be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, components, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and may be made without departing from the spirit and scope disclosed herein. 

What is claimed is:
 1. An optical bus for a dense wavelength-division multiplexing (DWDM) network, the optical bus comprising: an optical source configured to generate a plurality of unmodulated optical signals each having a different wavelength; an optical multiplexer configured to multiplex the unmodulated optical signals to produce a combined, unmodulated optical signal, and to transmit the combined, unmodulated optical signal through an optical fiber; and a plurality of nodes connected in sequence to the output of the optical multiplexer.
 2. The optical bus of claim 1, wherein each of the plurality of the nodes is not equipped with an optical source.
 3. The optical bus of claim 2, wherein each of the plurality of the nodes is equipped with a plurality of optical receivers each configured to detect a respective wavelength of an optical signal.
 4. A dense wavelength-division multiplexing (DWDM) optical network comprising: at least two counter-propagating DWDM buses, each of which comprising: a laser bank configured to generate a plurality of unmodulated optical signals each having a different wavelength channel; an optical multiplexer configured to multiplex the unmodulated optical signals to produce a combined, unmodulated optical signal, and to transmit the combined, unmodulated optical signal through an optical fiber for transport through the network; a plurality of nodes connected in sequence to the optical fiber, each node comprising: an optical input port for receiving optical signals from the optical fiber comprising wavelength channels; one or more modulators coupled to the optical input port wherein each modulator is configured to modulate a respective first wavelength channel of the wavelength channels with respective data to produce a modulated first wavelength channel; and an optical output port configured to transmit a combination of the one or more modulated first wavelength channels with a subset of the wavelength channels on the optical fiber.
 5. The optical network of claim 4, further comprising: one or more receivers coupled to the optical input port through an optical power splitter wherein each receiver is configured to receive a portion of optical power of the wavelength channels.
 6. The optical network of claim 4, wherein a first node of the plurality of nodes is configured to demultiplex received wavelength channels, split a portion of optical power from each of the received wavelength channels to a respective receiver, send each of the received wavelength channels through one of the modulators, multiplex one or more of the received wavelength channels with one or more modulated wavelength channels to form the combined optical signal and transmit the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously. The optical network of claim 4, wherein each of the plurality of the nodes is not equipped with the laser bank.
 8. The optical network of claim 4, wherein each modulator of the one or more modulators has a transmitting state and a bypassing state and wherein an input signal to a modulator is not modulated when the modulator is in the bypassing state.
 9. The optical network of claim 8, wherein one of the respective first wavelength channels passes through a first modulator and a second modulator, and wherein the first and second modulators are located in separate nodes of the plurality of nodes in one of the DWDM buses.
 10. The optical network of claim 9, wherein only one of the first and second modulators is in the transmitting state at any given time, and the other of the first and second modulators is in the bypassing state at the given time.
 11. The optical network of claim 4, wherein one or more optical amplifiers are configured between two of the plurality of nodes or between the laser bank and a first of the plurality of nodes.
 12. The optical network of claim 4, wherein a first node of the plurality of nodes comprises a plurality of photonic circuits coupled to the optical fiber, wherein the plurality of photonic circuits are configured to split an input light from the optical source into two polarizations in separate waveguides, and process the two polarizations of the input light by two identical photonic circuits of the plurality of photonic circuits to generate desired modulation patterns for transmission of the optical signal in the network.
 13. The optical network of claim 4, wherein a first node of the plurality of nodes comprises a photonic circuit coupled to the optical fiber, wherein the photonic circuit is configured to be with active feedback to track a polarization of an input light from the optical source and to maintain the polarization to a desired direction.
 14. The optical network of claim 13, wherein an output from the photonic circuit is configured to be fed into a single modulator of the one or more modulators to generate desired modulation for transmission in the network.
 15. A method for communication in a dense wavelength-division multiplexing (DWDM) optical network, the method comprising: generating, by a laser bank, a plurality of unmodulated optical signals each having a different wavelength channel; multiplexing the unmodulated optical signals to produce a combined, unmodulated optical signal; transmitting the combined, unmodulated optical signal through an optical fiber for transport through the optical network to a plurality of nodes that are connected in sequence to the output of the optical multiplexer; receiving, by each of the plurality of nodes, the unmodulated optical signal from the optical fiber comprising wavelength channels; modulating, by each the plurality of nodes, a respective first wavelength channel of the wavelength channels with respective data to produce a modulated first wavelength channel; and transmitting, by each the plurality of nodes, a combination of the respective modulated first wavelength channel with a subset of the wavelength channels on the optical fiber.
 16. The method of claim 15, further comprising: demultiplexing the subset of wavelength channels, by a first node of the plurality of nodes; splitting, by the first node, a portion of optical power from each of the subset of the wavelength channels to a receiver; sending, by the first node, each of the subset of the wavelength channels through one or more modulators to produce modulated second wavelength channels; multiplexing, by the first node, the modulated second wavelength channels to form the combined optical signal; and transmitting, by the first node, the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.
 17. The method of claim 16, wherein each modulator of the one or more modulators has a transmitting state and a bypassing state and wherein an input signal to a modulator is not modulated when the modulator is in the bypassing state.
 18. The method of claim 17, wherein one of the respective first wavelength channels of the passes through a first modulator and a second modulator, and wherein the first and second modulators are located in separate nodes of the plurality of nodes in one direction of the optical signals transmission in the network.
 19. The method of claim 18, wherein only one of the first and second modulators is in the transmitting state at any given time, and the other of the first and second modulators is in the bypassing state at the given time.
 20. An optical network node connected in sequence to an optical fiber of an optical network deployed a dense wavelength-division multiplexing (DWDM) communication, comprising: an optical input port configured to receive unmodulated optical signals from the optical fiber comprising wavelength channels; one or more modulators coupled to the optical input port wherein each modulator is configured to modulate a respective first wavelength channel of the wavelength channels with respective data to produce a modulated first wavelength channel; one or more receivers coupled to the optical input port through an optical power splitter wherein each receiver is configured to receive a portion of optical power of the respective first wavelength channel of the wavelength channels; and an optical output port configured to transmit a combination of the one or more modulated first wavelength channels with a subset of the wavelength channels on the optical fiber.
 21. The optical network node of claim 20, wherein the optical network node further comprises a demultiplexer to demultiplex all wavelength channels, split the portion of the optical power from each of a subset of the wavelength channels to the one or more receivers, send each of a subset of the wavelength channels through a modulator, multiplex all the wavelength to form the combined optical signal and transmit the combined signal to other nodes of the plurality of nodes in sequence on the network simultaneously.
 22. The optical network node of claim 20, wherein each modulator of the one or more modulators has a transmitting state and a bypassing state and wherein an input signal to a modulator is not modulated when the modulator is in the bypassing state.
 23. The optical network node of claim 22, wherein one of the respective first wavelength channels passes through a first modulator and a second modulator, and wherein the first and second modulators are located in separate nodes of the plurality of nodes in one direction of the optical signals transmission in the network.
 24. The optical network node of claim 23, wherein only one of the first and second modulators is in the transmitting state at any given time, and the other of the first and second modulators is in the bypassing state at the given time.
 25. The optical network node of claim 20, wherein one or more optical amplifiers are configured between two of the plurality of nodes. 